The aim of this project is to study mechanisms of immunity, immunoregulation, immune evasion and immunopathology in schistosomiasis with the ultimate goals of developing an experimental vaccine suitable for human trials as well as understanding the pathogenesis of disease. In work completed this year, mice infected with S. mansoni were demonstrated to have a selective defect in their capacity to mount Th1 cytokine responses to a foreign antigen. Moreover, IL-10 a cytokine previously shown to be produced by these animals, was demonstrated to inhibit the capacity of activated macrophages to kill schistosome larvae. Studies on immunopathogenesis revealed that IL-2 depletion reduces both granuloma formation and fibrosis in S. mansoni infected mice while downregulating IL-5 but up-regulating IL-4 synthesis. The pattern of cytokine production in S. japonicum infected mice was found to closely mirror that previously observed in S. mansoni infected animals.